1. Field of the Invention
The present invention relates to a driving circuit, and more particularly, to a driving circuit adapted to a liquid crystal display panel and a driving controller capable of adjusting internal impedance thereof.
2. Description of the Related Art
Generally, a typical thin film transistor liquid crystal display (TFT-LCD) includes an upper panel having a color filter, a lower panel and liquid crystal filled between the upper panel and the lower panel. A plurality of scanning lines (gate lines) and a plurality of data lines (source lines) crossed above the plurality of scanning lines, are formed on the lower panel. A plurality of thin film transistors (TFT) arranged in an array, are adjacent to intersections defined by the scanning lines and the data lines respectively. Each TFT is configured for determining whether or not transmit a data signal of the corresponding data line electrically connected to this TFT, to a corresponding pixel, according to a controlling signal of the corresponding scanning line electrically connected to this TFT. Therefore, each TFT is used as a switch for the corresponding pixel.
FIG. 1 is a circuit block diagram of a typical liquid crystal display (LCD) panel. As shown in FIG. 1, a TFT-LCD panel 10 includes a board 12, a printed circuit board 14 and a plurality of flexible printed circuit boards 16. The flexible printed circuit boards 16 are electrically coupled between the printed circuit board 14 and the board 12. The printed circuit board 14 includes essential electronic members, such as a power supply (not shown) and a time controller (not shown), etc., formed thereon. A plurality of scanning lines GL1, GL2, . . . GLm, and a plurality of data lines DL1, DL2, . . . DLn, are formed on the board 12. The plurality of scanning lines GL1, GL2, . . . GLm, are crossed above or below the plurality of data lines DL1, DL2, . . . DLn, to define a pixel array in an active region 122 of the board 12. A plurality of source driving controllers 18 are arranged on a periphery region of the board 12 electrically connected to the flexible printed circuit boards 16. The source driving controllers 18 are electrically connected to the flexible printed circuit boards 16 for receiving data signals to drive the data lines DL1, DL2, . . . DLn. Similarly, a plurality of scanning driving controllers 22 are arranged on another periphery region of the board 12 for receiving control signals to drive the scanning lines GL1, GL2, . . . GLm.
The power supply of the printed circuit board 14 provides power voltages (for example, analog power voltages) to the source driving controllers 18 and the scanning driving controllers 22 via conductive paths 19 and 23, respectively. The conductive paths 19 and 23 are formed directly on the surface of the board 12, those called as a mode of wiring on array (WOA). As shown in FIG. 1, the conductive path 19 provides the power voltages to the source driving controllers 18 in a cascade frame, such that the power voltages are transmitted along a single direction. However, if the mode of wiring on array is used in the board 12 made of glass, the resistance of the wires is high and a large change of the voltage drop is produced. Therefore, the plurality of flexible printed circuit boards 16 should be employed, for solving the problem in relation to the differences of the input voltages (working voltages) of the source driving controllers 18 in the cascade frame. If the plurality of flexible printed circuit boards 16 are employed, the conductive path 19 will not be too long and the change of the voltage drop is decreased.
However, the manufacturing cost is high since employing the plurality of flexible printed circuit board. To decrease the manufacturing cost, there should have as few flexible printed circuit boards (for example, only one flexible printed circuit board) as possible. Furthermore, the input voltages of the driving controllers should be substantially same.
What is needed is providing a driving circuit, which can solve the above problems.